Access Method And Apparatus That Limit Motion According To Load And Position

ABSTRACT

A hydraulic drive system for an access apparatus and a method of access is presented. The hydraulic drive system may include a hydraulic power unit, a hydraulic cylinder and a subsystem for limiting motion of the access system according to the position of and/or load supported by the access system. The subsystem may prevent motion, such as stowing and/or folding, when the access apparatus is supporting a load and/or is in a predetermined position. To limit motion, the subsystem may create a fluid path from the hydraulic power unit that bypasses the hydraulic cylinder, thus preventing the cylinder from moving the access apparatus. The subsystem may include a first valve that is opened when the access apparatus is in the predetermined position, and/or a second valve that is opened when the access apparatus is supporting a load.

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 60/573,614, filed on May 21, 2004,which is hereby incorporated by reference.

BACKGROUND

Access systems or apparatuses such as wheelchair lifts assistmobility-challenged individuals. For example, parallelogram-type liftsmay be used with vehicles in personal and public (such as, paratransit)mobility applications. Such parallelogram-type lifts may use a hydraulicsystem to move a transfer member, which may include a lift, betweenthree positions including stowed (which may included folding), transferlevel (such as the floor level of a vehicle or the level of othersurfaces), and ground level positions. Such hydraulic systems may takeadvantage of gravity to lower the lift transfer member from the transferlevel to the ground level. This “gravity down” or “gravity assist”feature may conserve power and reduce the wear on the components of thehydraulic system, such as the hydraulic pump and motor. The gravity downfeature, which may include unfolding and lowering operations, may becontrolled by throttling the hydraulic fluid flow by using, for example,flow restrictors, actuatable valves, and the like to limit free-fall ofthe lift and provide smooth motion of the lift transfer member,particularly when transferring a user between the transfer and groundpositions. In such hydraulic systems, the motor and hydraulic pump mayoperate to raise the transfer member from the ground level to thetransfer level, and to move the transfer member into a stowed position.

Access systems or apparatuses may include safety systems to ensure thewell being of access apparatus users. The National HighwayTransportation Safety Administration (NHTSA) has adopted rules mandatingthe implementation of safety systems, such as “interlocks.” One type ofinterlock prevents the access apparatus from being stowed when thetransfer member is occupied. To detect whether the transfer member isoccupied, a safety system may include mechanical, electrical, orelectromechanical sensors. An example of such a sensor includes ahydraulic pressure switch, which may be set or calibrated to detectpressures over a predetermined threshold that are indicative of a loadon the transfer member. For example, the threshold may equal about 50pounds. When the hydraulic pressure switch detects a pressure aboutequal to or greater than the threshold, the switch changes states todisconnect the pump motor from a power source.

The use of a hydraulic pressure switch has disadvantages. In somecircumstances, such as when the motor is energized to start stowing thetransfer member, the pump generally needs to run for a time period topressurize the hydraulic system before the pressure switch can detectwhether the transfer member is occupied. During this time period,however, the pump may build up sufficient pressure in the system toinitiate stowing of the transfer member, even if the transfer member isoccupied. Further, the access system may continue to stow the transfermember after the pump has been shut off until the hydraulic systemreaches a steady state. Steady state may be reached, for example, whenthe pressure in the system becomes balanced with that of a loadsupported by the transfer member. Additionally, if the system pressuredrops below the threshold when the pump is deactivated, the hydraulicpressure switch may again turn on the pump causing erratic or pulsatingoperation of the access system. Such operation may lead to pressurespikes, which may damage the components of the hydraulic system.Moreover, such operation may be disconcerting to an occupant of theaccess system, and may cause the occupant to fall from the accesssystem.

SUMMARY

In view of the foregoing, there exists a need for a hydraulic drivesystem (and an access apparatus and method of access, which use thedrive system) for limiting motion, such as that associated with stowingor folding an access apparatus, according to the load on and/or positionof the access apparatus. The hydraulic drive system may include ahydraulic power unit, a hydraulic cylinder and a subsystem for limitingmotion according to load and/or position. The hydraulic power unitsupplies fluid to the hydraulic cylinder so that the hydraulic cylindermay move the access apparatus. Under certain circumstances, thesubsystem creates a fluid path from the hydraulic power unit thatbypasses the hydraulic cylinder, thus preventing the cylinder frommoving the access system.

The subsystem may include a first valve, such as an electricallyactuated valve, which opens when the access system is in a predeterminedposition. The first valve may be solenoid driven and in communicationwith a position sensor, such as a cam and microswitch arrangement, whichdetermines the position of the access apparatus. The position sensor mayopen the first switch when the access apparatus is in a predeterminedposition. The subsystem may also include a second valve, which may be influid communication with the first valve. The second valve may include alimit pressure that, if exceeded, creates a fluid path that bypasses thehydraulic cylinder, thus preventing the cylinder from moving the accessapparatus. The pressure limit may include a value less than the pressurerequired by the cylinder to move the access apparatus when the accessapparatus supports a load. Additionally, or alternatively, the pressurelimit may include a value greater than the pressure required by thecylinder to move the access apparatus when the access apparatus is notsupporting a load, thus allowing the access apparatus to be stowed.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the following figures are not necessarily to scale,emphasis instead being placed upon illustrating the associatedprinciples. In the figures, the same reference symbols designate thesame parts, components, modules or steps, unless and to the extentindicated otherwise.

FIG. 1 is an isometric view of an access apparatus installed in avehicle; and

FIG. 2 is a schematic diagram of a hydraulic drive system of the accessapparatus of FIG. 1.

DETAILED DESCRIPTION

An exemplary access system is shown in FIG. 1. In this example, theaccess system 10, such as a dual parallelogram type lift, includes atransfer member 12 and is installed in a vehicle V, such as a bus, vanor automobile. However, the access system 10 may be installed on or nearany structure to which access is desired. Access system 10 may beinstalled in a doorway D and bolted or otherwise attached to a floor,such as a vehicle floor F. Access system 10 is operable to enable amobility-challenged individual using a wheelchair, scooter, walker orother mobility assistance device to enter and exit a vehicle V or accessa structure. The individual may enter the access system 10 via transfermember 12, which transfers the individual from one level (“groundlevel”) to another level (the “transfer level” or “transfer position”),such as the level of the vehicle doorway D.

The access system 10 may include several features that enhance thesafety of an individual during transfer. Exemplary safety featuresinclude one or more of the following: graspable handrails 18, an inboardbarrier 16, and an outboard barrier 14. With reference to the axis shownin FIG. 1, a direction closest to or toward the transfer level, such asthat of the vehicle V, shall be referred to as inboard (IB), whereas thedirection away or farthest from the transfer level shall be referred toas outboard (OB). Inboard and outboard barriers 16 and 14 may includeroll stops, which are operable to prevent an individual fromaccidentally falling off the transfer member 12 when the transfer member12 is elevated above ground level. The barriers 14, 16 may be actuatedby various apparatuses including, for example, mechanical, electrical,and electromechanical devices and/or systems. The inboard barrier 16 maybe actuated by a mechanical linkage system, whereas the outboard barrier14 may be actuated by a hydraulic cylinder (not shown). In addition, theinboard barrier 16 may serve as a “bridge plate” to allow the individualto safely enter and exit the transfer member 12 at the transfer level.Controls for the access system 10 may be located within or outside ofthe vehicle V or other structure and may be manipulated by a liftoperator, such as the vehicle driver. Controls for the access system 10may include switches, buttons or the like, which are operable to raise,lower, deploy, and/or stow the transfer member 12. When the doorway D isclosed and the vehicle V is in motion, the access system 10 is generallystowed such that the transfer member 12 is folded and stored withinvehicle doorway D. When the doorway D is unobstructed by, for example, adoor or other object and the vehicle V is in a secure state, the accesssystem 10 may be deployed and/or unfolded.

The access system 10 may include or be in communication with anelectrical system (not shown). The access system 10 may be powered by avehicle's power source, which may include a battery and alternator, abuilding's power supply, or other fixed or portable power supply.Alternatively, the access system 10 may include or be in communicationwith a dedicated power source, such as a battery. The access system 10may include a hydraulic drive system 300, which may include a motorizedpump 305 that provides fluid to lifting cylinders 307 that stow orotherwise move the access system 10. Stowing the access system 10 mayinclude raising and/or folding the transfer member 12. The motorizedpump may be linked to the power source by a switch or the like thatturns the pump on and off. The electrical system may include variousswitches and relays for operating the access system 10 relative to statechanges of the switches as the access system 10 operates. The accesssystem 10 may include a control system, which may include a controlboard, logic board, or electronic controller. The electrical system mayinclude a control panel or hand control (not shown) for actuating theaccess system 10 to stow, deploy, lower, raise or otherwise move thetransfer member 12. The controls for stowing, deploying, lowering,raising or otherwise moving the transfer member 12 may include rockerswitches, buttons, or the like, which may be manipulated by the accesssystem operator. Additionally, the electrical system may include one ormore sensors for detecting various states of the access system 10 and/orpositions and/or elevation of the transfer member 12 (such as ground,transfer and other positions). Such sensors may include microswitches,Hall effect sensors, and other sensing devices and/or systems. Thesensors may include a microswitch that is cam actuated when the transfermember 12 reaches the transfer level. Actuation of the microswitch mayautomatically switch off power to the motor to prevent damage andunnecessary wear to the access system 10 when the transfer member 12 israised to the transfer level. In response to signals from sensors and/orcontrols, various elements of the access system 10 such as motors andvalves may be actuated or deactuated.

An exemplary hydraulic drive system 300 is shown in FIG. 2, which mayinclude a fold limiting system that inhibits stowage of the accesssystem 10 when the transfer member 12 is occupied. The hydraulic drivesystem 300 may also include a pump 305 driven by an electric motor 310to act on one or more hydraulic cylinders 307 for raising and stowingthe access system 10. As shown in FIG. 1, the access system 10 mayinclude two cylinders 307, each of which may be disposed within theaccess system's 10 lifting structures. As shown in FIG. 2, the pump 305may be in communication with a reservoir 315. The pump 305, motor 310,and reservoir 315 may be integrated with other hydraulic components,such as pressure relief valves and/or directional valves in the form ofa valve manifold, to form a hydraulic power unit.

The hydraulic power unit 300 may include a first pressure relief valve320 and a check valve 325, both of which are generally related to theraising operation of the access system 10. The first pressure reliefvalve 320 is set or otherwise operative to limit the output pressure ofthe pump 305. This may prevent damage to the motor 310 and otherhydraulic system components if, for example, one of the cylinders 307 orthe check valve 325 binds or freezes. Towards this end, the firstpressure relief valve 320 may include a limit pressure. For example, thelimit pressure may equal about 1800 pounds per square inch (“psi”).Check valve 325 is operative to maintain the pressure of fluid pumped tothe cylinders 307, which inhibits the transfer member 12 from loweringwhen the pump 305 stops (such as when the transfer member 12 reaches thetransfer level). The hydraulic drive system 300 may also include a firstelectrically actuated valve 327 that is related to the lowering orgravity down/assist operation of the access system 10. The firstelectrically actuated valve 327 may include a 2 way, 2 position normallyclosed solenoid actuated valve that prevents hydraulic fluid fromflowing into the reservoir unless a lowering operation of the transfermember 12 is activated. Upon such activation, the access system 10energizes the down valve 327, thereby permitting fluid to flow from therod side of the cylinders 307 through the valve 327 and to the reservoir315, thus extending the cylinders' rods outward as the transfer member12 lowers under gravity.

Additionally, the hydraulic drive system 300 may include a manuallyoperated backup system 330 that facilitates use of the access system 10without electrical power, for example, in the event of a power failure.The backup system 330 may include a manually actuated pump 332 withcheck valves 334, 336, a pressure relief valve 338, and a manual shutoffvalve 340. The backup system 330 may facilitate lowering the transfermember 10 via gravity, and/or raising an unloaded transfer member 12 sothat it may be stowed.

Furthermore, the hydraulic drive system 300 may include a fold limitingsystem. The fold limiting system may include a second electricallyactuated valve 342 (the “electrically activated fold valve”) and asecond relief valve 344 (the “fold relief valve”) that may be inlinewith the second activated valve 342. The valves 342, 344 may contributeto the folding operation of the access system 10. The access system 10,through an electrical interface, may utilize the electrically activatedfold valve 342 to establish a hydraulic fluid path with the fold reliefvalve 344.

The electrically actuated fold valve 342 may include a 2 way, 2 positionnormally closed solenoid actuated valve that prevents hydraulic fluidfrom flowing into the reservoir unless the valve 342 is energized. Thefold relief valve 344 is set or otherwise operative to limit the outputpressure of the pump 305 when the electrically activated fold valve 342is energized. The limit pressure (P_(limit)) of the fold relief valve344 may include a predetermined value that is slightly greater than thepressure required to fold the transfer member 12 when the transfermember 12 is empty (“P_(fold-empty)”). P_(fold-empty) may include avalue in the range of about 400 psi to about 500 psi. Thus, when thetransfer member 12 is unloaded, the pump 305 will build up pressure inthe hydraulic drive system 300 until the pressure is sufficient to stowthe access system 10 (in other words, the pressure reaches aboutP_(fold-empty)). Because P_(fold-empty) is less than P_(limit), therelief valve 344 will remain closed (for example, because P_(fold-empty)cannot overcome the force of the valve's spring biased poppet) and thelift transfer member 12 will be folded. Hydraulic fluid will not bepermitted to flow to reservoir 315 through valve 344, but will flow fromthe pump 305 to the cylinders 307 to stow the access system 10.

However, when the transfer member 12 is positioned at the transferlevel, the pressure downstream of the check valve 325 is substantiallylower than the pressure in the cylinders 307. Consequently, the pressurebuild up may not be strictly linear and the pump 305 may introducepressure spikes in the system 300 until a steady-state pressure isachieved. Such pressure spikes may include a range from about 1700 psito about 1900 psi, which may be sufficient to initiate stowing of theaccess system 10. To this end, the limit pressure P_(limit) of the foldrelief valve 344 is selected so that momentary spikes of pressuregreater than P_(limit) open fold relief valve 344 causing the fluid tobypass the cylinders 307 and go to the reservoir 315. This prevents thetransfer member 12 from being stowed before a steady state pressure isachieved. The P_(limit) of the fold relief valve 344 may be about 550psi.

Further, P_(limit) may be selected so that when a predetermined typicalminimum load (such as an object weighing about 50 pounds) is on thetransfer member 12, the access system 10 is inhibited from stowing. Inthis way, if the transfer member 12 is occupied by a load, such as awheelchair and/or occupant, the pump 305 must generate a steady statepressure incrementally greater than the pressure required to fold thetransfer member 12 when empty (P_(fold-empty)). Thus,P_(fold-occupied)=P_(fold-empty)+ΔP)>>P_(limit) and the incrementalpressure increase is bypassed to the reservoir 315 via valves 342, 344thereby preventing the occupied transfer member 12 from tilting inwards.Because the folding pressure for stowing the occupied lift transfermember (P_(fold-occupied)) is greater than the limit pressure(P_(limit)) of relief valve 344, the valve 344 will be opened (because,for example, the folding pressure is greater than the force of thevalve's spring biased poppet and forces the poppet open), therebycreating a fluid path from the pump 305 to the reservoir 315, whichbypasses the cylinders 307. Thus, the fluid that is not bypassed to thereservoir 315 by valves 342, 344 will have a lower pressure than thatgenerated by the pump 305 and will be inadequate to overcome the weightof the transfer member 12 and the load supported by the transfer member12 so that the rods of cylinders 307 remain static and the transfermember 12 is inhibited from stowing.

Before a stowing operation is actuated (for example, by pressing abutton or switch on a hand controller) and the access system 10 startsto move, the electrical system actuates the fold valve 342. Whenactuated, the fold valve 342 is open and fluid output by the pump 305bypasses the cylinders 307 and goes to the reservoir 315 if the pumpoutput pressure is greater than the limit pressure of the fold reliefvalve. The access system 10 may include one or more sensors and/orswitches operative to sense the transfer member 12. The sensor may beoperative to detect when the transfer member 12 is positioned at apredetermined level, such as the transfer level. For example, the sensormay energize the fold valve 342 when the transfer member 12 reaches thepredetermined level. The sensor may include a microswitch with normallyopen and normally closed terminals such that the switch is cammed whenthe transfer member 12 is positioned at the predetermined level.Thereby, the switch simultaneously switches off power to the motor 310and switches on power to the electrically activated fold valve 342.Thereafter, if a stowing operation is actuated and the transfer member12 is supporting a load, the hydraulic pressure at the pump output isovercome by the load such that the transfer member 12 remainsstationary.

When the access system 10 is actuated to lower the transfer member 12from the predetermined level, the fold valve 342 and the firstelectrically activated valve 327 are closed to allow the fluid to drainfrom the lift cylinders 307. This permits the transfer member 12 tolower under gravity power. If the access system 10 is actuated to stowthe transfer member 12, or if the motor 310 cannot be de-energizedbecause, for example the hand control malfunctions, the fold-limitingsystem will prevent the transfer member from moving although the motor310 and pump 305 operate normally. When the transfer member 12 reachesthe predetermined level, the access system 10 may energize the foldvalve 342 and the pump 305 may continue to run. However, the pump 304will not build up sufficient pressure in the system to stow the accesssystem 10. Thus, the fold-limiting system may provide safeguards againstmalfunctioning of the hydraulic and/or electrical systems.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of theinvention. For example, the hydraulic system may include a proportionalvalve linked to the controller to provide real-time dynamic feedbackcontrol of the lift. Accordingly, the invention is not to be restrictedexcept in light of the attached claims and their equivalents.

1. A hydraulic drive system for an access apparatus, comprising: ahydraulic power unit configured to supply fluid; a hydraulic cylinder influid communication with the hydraulic power unit and configured to movethe access apparatus in response to the fluid; and a subsystem in fluidcommunication with the hydraulic power unit and configured to preventthe hydraulic power unit from moving the hydraulic cylinder when theaccess apparatus supports a load.
 2. The hydraulic drive system of claim1, wherein the subsystem includes a fluid path configured to bypass thehydraulic cylinder.
 3. The hydraulic drive system of claim 1, whereinthe subsystem includes a first valve in fluid communication with thehydraulic power unit and configured to open when activated.
 4. Thehydraulic drive system of claim 3, wherein the first valve is furtherconfigured to be activated when the access apparatus is positioned at apredetermined level.
 5. The hydraulic drive system of claim 1, whereinthe subsystem includes a second valve in fluid communication with thehydraulic power unit and configured to bypass the hydraulic cylinderwhen the access apparatus supports the load.
 6. The hydraulic drivesystem of claim 5, wherein the second valve includes a limit pressureand is further configured to bypass the hydraulic cylinder when apressure of the fluid meets or exceeds the limit pressure.
 7. Thehydraulic drive system of claim 5, wherein the second valve includes alimit pressure with a value lower than a pressure required by thecylinder to move the access apparatus when the access apparatus supportsthe load.
 8. The hydraulic drive system of claim 5, wherein the secondvalve includes a limit pressure with a value higher than a pressurerequired by the cylinder to move the access apparatus when the accessapparatus does not support the load.
 9. The hydraulic drive system ofclaim 8, wherein the limit pressure is about 550 psi.
 10. The hydraulicdrive system of claim 8, wherein the pressure required by the cylinderto move the access apparatus when the access apparatus does not supportthe load is from about 400 psi to about 500 psi.
 11. A hydraulic drivesystem for an access apparatus, comprising: a hydraulic power unitconfigured to supply fluid; a hydraulic cylinder in fluid communicationwith the hydraulic power unit and configured to move the accessapparatus in response to the fluid; and a subsystem configured to bypassthe hydraulic cylinder when the access apparatus supports a load, thesubsystem comprising: a first valve in fluid communication with thehydraulic power unit and configured to open when the access apparatus ispositioned at a predetermined level; and a second valve including alimit pressure, in fluid communication with the first valve, andconfigured to bypass the hydraulic cylinder when a pressure of the fluidreceived from the first valve meets or exceeds the limit pressure. 12.An access system, comprising: a transfer member configured to support aload; and a hydraulic drive system coupled with the transfer member andincluding: a hydraulic power unit configured to supply fluid; ahydraulic cylinder in fluid communication with the hydraulic power unitand configured to move the access system in response to the fluid; and asubsystem in fluid communication with the hydraulic power unit, andconfigured to prevent the hydraulic power unit from moving the hydrauliccylinder when the access system supports the load.
 13. The access systemof claim 12, further comprising a sensor configured to determine aposition of the transfer member and communicate the position of thetransfer member to the subsystem.
 14. The access system of claim 13,wherein the subsystem is further configured to prevent the hydraulicpower unit from moving the hydraulic cylinder according to the positionof the transfer member.
 15. A method for providing access to apredetermined level, the method comprising: providing a transfer memberconfigured to support a load; and providing a hydraulic drive systemcoupled with the transfer member and including: a hydraulic power unitconfigured to supply fluid; a hydraulic cylinder in fluid communicationwith the hydraulic power unit and configured to move the access systemin response to the fluid; and a subsystem in fluid communication withthe hydraulic power unit, and configured to prevent the hydraulic powerunit from moving the hydraulic cylinder when the access system supportsthe load.
 16. A hydraulic drive system for a lift, the lift including asensor for detecting a position of the lift, the hydraulic drive systemcomprising: a hydraulic power unit; and a subsystem including a limitpressure, and configured to prevent movement of the lift according tothe position of the lift, wherein the subsystem is in fluidcommunication with the hydraulic power unit, and in communication withthe sensor.
 17. The hydraulic drive system of claim 16, wherein thesubsystem is further configured to prevent movement of the liftaccording to a load supported by the lift.
 18. The hydraulic drivesystem of claim 16, further comprising a hydraulic cylinder and thesubsystem includes a fluid path configured to bypass the hydrauliccylinder.
 19. The hydraulic drive system of claim 16, wherein thesubsystem includes a first valve in fluid communication with thehydraulic power unit and configured to open according to the position ofthe lift.
 20. The hydraulic drive system of claim 16, wherein thesubsystem includes a second valve in fluid communication with thehydraulic power unit and configured to open when the lift supports aload.